The height control sensor is just in front of the driver'* rear tire. If you put the car up on a stand and pull the tire, you can access everything from below. The sensor is bolted (just 1) to the subframe and has a small rod running from it to the lower control arm (another bolt) if memory serves. There is also an electrical line that runs to a connector on the other side of the subframe.

I was confident I found the problem when I removed the rod connecting them and moved it myself so I could hear the pump turn on and off. I did this with both airlines pulled out of the shocks so the car didn't change height while it was jacked up on stands.

Once the tire was off, it took about 10 minutes to remove, install, connect electrical then plug in the airlines. I can't think of any repair I have done that was easier.